tests/test-diff-newlines.t

tests: add test coverage for lfdirstate invalidation of linear update

f72d73937853 introduced a significant performance regression: All largefiles
are marked 'normallookup' in lfdirstate by linear (or noop) updates and has to
be rehashed by the next command.

To avoid such regressions, keep an eye on the dirstate content after a plain
'hg up'.

  $ hg init

  $ $PYTHON -c 'file("a", "wb").write("confuse str.splitlines\nembedded\rnewline\n")'
  $ hg ci -Ama -d '1 0'
  adding a

  $ echo clean diff >> a
  $ hg ci -mb -d '2 0'

  $ hg diff -r0 -r1
  diff -r 107ba6f817b5 -r 310ce7989cdc a
  --- a/a	Thu Jan 01 00:00:01 1970 +0000
  +++ b/a	Thu Jan 01 00:00:02 1970 +0000
  @@ -1,2 +1,3 @@
   confuse str.splitlines
   embedded\r (no-eol) (esc)
  newline
  +clean diff